1. Field of the Invention
The present invention relates to an apparatus for measuring a bulk stream.
2. Description of the Related Art
A number of apparatus are already known for directly measuring bulk streams, i.e. a mass-time unit. One class of these apparatus is based on the principle of measuring that force which must be expended to impress a definite angular velocity or tangential velocity component on a bulk stream flowing linearly through a conduit. The necessary force is directly proportional to the bulk stream. The following relation holds: EQU torque=k.multidot.angular velocity.multidot.bulk stream
If the angular velocity is thus kept constant, the bulk stream is a linear function of the torque.
Apparatus are already known for measuring the flow rate of bulk material wherein the bulk material is directed axially onto a rotary plate bordered by radially extending guide blades. The rotary plate is driven by a synchronous motor at a constant motor speed and the driving torque measured. The change in this torque is a direct measure of the fluctuations in the bulk stream.
Different solutions are known for measuring this torque. The most simple solution consists in measuring the power consumption of the motor. However, this method yields quite imprecise results since the measuring result also includes all succeeding, constantly changing frictional losses both in the motor and in a set of gears which may follow (German utility model No. 70 23 502).
Picking up the torque directly from the driving shaft of the rotary plate has also proved to be disadvantageous since the measured values must be picked up from the rotating shaft via brush type contacts, which leads to a high susceptibility to disturbance under rough operating conditions (U.S. Pat. No. 2,934,951).
It is also known to arrange the driving motor for the rotary plate directly below the rotary plate and pivot the motor about its driving axle. Torsion of the motor housing is monitored by an arm protruding into a moving coil and attached to the motor housing. The reaction torque corresponding to the driving torque seeks to turn the motor housing around. This torsion is compensated by an electromagnetic force exerted by the moving coil on the arm. This force, which constantly holds the motor housing in a definite desired position, is proportional to the current consumption of the moving coil. The value of this current is thus a measure of the mass flowing over the rotary plate per unit of time (German Pat. No. 1 211 415). This solution is not practicable if only because the driving motors required to accelerate high bulk streams have a large inert mass which can only be adjusted to a definite desired position by generating high electromagnetic forces. However, if the controlling torque is so high small fluctuations in the measurable variable can no longer be observed reliably enough. The known solution furthermore does not allow for a set of gears to be inserted.
An apparatus is also known (U.S. Pat. No. 2,771,773) in which the torque is measured which is exerted on the intermediate shaft of a set of gears disposed between the driving motor and the rotary plate. The intermediate shaft of the spur gear is mounted in the shank whose lower end is suspended such that the shank can be swivelled about an axis directed perpendicular to the axis of the gearwheels and located on a plane parallel to the gearwheels. The swivelling axis of the shank for the intermediate shaft is furthermore arranged such that the shank is tilted out of the plane of action of the teeth by the driving pinion together with the intermediate shaft and the intermediate gearwheel. This displacement is counteracted by a spring which compensates no more than the no-load torque. If a larger torque is transmitted when a bulk stream acts upon the rotary plate, the shank is held in its position pneumatically. The pressure required therefor, which is read off an appropriate measuring instrument, is again a measure of the transmitted torque.
The disadvantage of this apparatus is in particular the long idle time which necessarily passes until a measured value is displayed after the compensating pneumatic pressure is adjusted. It is not possible to regulate pulsating streams of bulk material using the known apparatus. Furthermore, the regulating apparatus is elaborate and the susceptibility to trouble is accordingly high.
Most recently, chemical and metallurgical methods have been developed by which powdery or fine-grained substances are made to react with each other or with liquid or gaseous substances in a precisely defined stoichiometric ratio in a continuous process. Examples of this are the gasification of coal and the melt reduction of iron ores. These methods require that the bulk streams of several components be coordinated, which presupposes the measurement and regulation of these bulk streams. As already explained above, the main problem consists in measuring the torque or braking moment (n.multidot.m) precisely enough. The shaft of the rotating element is naturally slowed down not only by the stream of material but also by frictional forces. These frictional forces change considerably when the temperature fluctuates since the viscosity of the lubricants required for the shaft bearing changes.